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Considerable amount of research work has recently been performed in the area of wireless sensor networks. In this paper we address the diversity of programming interfaces for link layer information as well as sensor measurement data as one of the few critical problems that have not in our opinion been addressed thoroughly enough. We propose the use of the unified link-layer API (ULLA) for wireless sensor networks. It offers a common interface to retrieve link layer information independently of the deployed radio technology considerably simplifying development process of link-aware protocols and applications. The ULLA can be used not only by applications running locally on sensor nodes but also remotely by applications running in an end-user device. Additionally, ULLA allows to retrieve sensor readings via the same convenient interface. The interface offers a powerful notification mechanism, which can be used to monitor the sensor network and trigger certain actions when either the communication environment changed, for instance an ad hoc route disappeared, or the sensor readings pass a threshold, e.g. usable for fire-alarm. These features essentially generalize the approach taken by TinyDB to include link-layer information as well, and further extend the abstraction of the sensor network as a database. A prototype implementation of ULLA on Telos B motes has been made to demonstrate the feasibility of the ULLA approach. The footprint of the implementation is very acceptable, and performance offered sufficient even for protocols taking per-packet decisions based on link conditions. The ULLA implementation is available from http://tinyos.cvs.sourceforge.net/tinyos/tinyos-1.x/contrib/rwth/mobnets/.